1. Field of the Invention
This invention generally relates to electrical connectors and contacts for use therein and, particularly, to an improvement of retention and flexibility of the contact for the SIMM socket.
2. The Prior Art
Single in-line memory modules, i.e. "SIMM", the most popular components used in PC industry presently, represent a high density, low profile single in-line package for electronic components such as RAM integrated circuit components. For achieving high density arrangement of contacts, instead of using stamped and formed contacts, most current designs employ edge stamped contacts because the width of the former generally precludes establishing an interconnection on closer center line spacings.
Two problems follow this alternative. First, the edge stamped contact inherently has an inferior spring character to the formed contact; in other words, it is more critical to design the shape of the edge stamped contact for obtaining a sufficient retention force therebetween but still maintaining a Zero Insertion Force (ZIF) or Low Insertion Force (LIF) feature for the complementary module inserted within the socket. Moreover, the thickness of the module board received within the socket may alter in a range from 1.19 mm to 1.37 mm, so the space between two contact beams of the contact should be maintained within a proper range by which the contact can effectively engage the thinnest module board but still have a good resilience character to spring out for retractably and properly engaging the thickest module board without any permanent deformation.
The other problem is to provide the contact with a sufficient retention force within the socket without exerting a large amount of reaction or friction force during insertion of the contact into the socket.
Regarding the first issue, dissatisfaction has been found in U.S. Pat. Nos. 4,737,120 to Grabbe and 5,015,196 to Yamada which disclose each contact sandwiches an edge of a module board therein. Because they are both of the top-loading type in the housing, there is no possibility to position an engaging means on the housing in the space between two contact beams to engage the contact beam of the contact to store preloaded resilience thereof beforehand, when the module board is not inserted into the socket, for better engagement with the module board. That is, to those type contacts, the flexibility of the beams of the contact is limited and the range of accommodating variation of the module thickness is narrowed. As disclosed in U.S. Pat. Nos. 4,946,403 and 5,041,005, some attempts have been made to improve this shortcoming by using a bottom-loading contact which cooperates with engaging means of the socket to perform high deflection so as to meet the board range of variation of the module thickness.
Regarding the second issue, as disclosed in U.S. Pat. Nos. 4,713,013, 4,718,859, 4,946,403, 4,957,448, 4,960,386, 5,009,611 and 5,041,005, there are several types of retention means of the contact for securement in the socket. A general rule can be found in those designs that to obtain a stronger retention in the socket, a strong interference fit between the contact retention section and the socket is desired so that a larger force is required to insert the contact into the socket. Consequently, a expensive stronger material is preferred to form the contacts because the retention section should be stiff enough to endure the friction force exerted thereon during insertion of the contact into the socket. Also, the larger force inserting the contacts into the socket and imposed on the contacts and the socket, may damage or tilt the corresponding components .
Accordingly, this invention is directed to providing a SIMM socket having therein contacts of which, cooperating with the socket, each has a retention section which can engage the socket in an enhanced interference fit but easily pass therethrough without a larger insertion force before it reaches its final position.
Another object of the invention is to provide the contact with the retention section which is located between two beams of the contact so that a better balance for securement can be achieved when two beams engage two sides of the lower portion of the module board, respectively.
Yet, another object of the invention is to provide the contact with the retention section which is totally hidden within the socket for better securement without any external factor's effect.
Still, another object of the invention is to provide the contact with high deflection for accommodating a broad range of board thickness.